In a semiconductor device manufacturing process, a process for forming a hole or a trench in laminated films formed on a semiconductor wafer (hereinafter, referred to as a “wafer”) through a resist mask formed on the laminated films by using single etching apparatus is being examined, in which an etching gas corresponding to each film is employed. In such process, after the laminated films are formed on the wafer, a peripheral portion thereof is removed by a wet cleaning apparatus and, then, a resist pattern is formed on the remaining laminated films. Therefore, when the wafer is etched, silicon as a base material is exposed at the peripheral portion of the wafer. Accordingly, the silicon of the peripheral portion of the wafer is cut by the etching process, and acute protrusions of a needle shape are densely formed at the surface thereof. Since a plasma is not ejected on the peripheral portion of the backside of the wafer, a reaction product, e.g., polymer, generated by the reaction between the laminated films and the plasma on the wafer surface is deposited thereon, and thus undesired particles may be generated.
Acute silicon irregularities (the protrusions of needle shape) formed at the peripheral portion of the wafer surface are not easily removed by plasma cleaning due to the anisotropic property of the plasma of the cleaning gas. The protrusions cannot be scraped off by brush cleaning. Although the protrusions can be removed by CMP (Chemical Mechanical Polishing), the wafer surface may be contaminated. The deposit adhered to the peripheral portion of the backside of the wafer contains a plurality of materials. Hence, when dry cleaning (plasma cleaning) is performed, a cleaning gas needs to be changed depending on materials of the films. However, it is difficult to process only the peripheral portion of the wafer, and the device area of the wafer is damaged. When wet etching is performed, the same problems are generated, and the re-adhesion of the removed deposit occurs.
Meanwhile, International Patent Application Publication No. 2010/021265 (WO/2010/021265) describes a technique for etching or planarizing a semiconductor substrate or a thin film formed thereon by ejecting gas clusters thereto without ionizing the gas clusters. However, WO/2010/021265 does not describe a technique for cleaning the peripheral portion of the wafer.